1. Methods for preserving algal cells for a long period without significant loss of growth capacity were examined. 2. Blue-green algae, Tolypothrix tenuis and Calothrix brevissima, could be preserved for 2 years in the lyophilized state with only a loss of about fifty percent in activity, if the Fifth Fraction of human serum albumin was provided as a protective substance. 3. As a practical method for preserving a large quantity of algae, a method of adsorption on a special fine porous gravel (Kanuma-tsuchi) was devised. The algae cultured on its moist surface were found to retain the capacity for growth being almost unimpaired for at least 2 years.